Resposta :
A 4,2 = 12 , ISSO QUER DIZER QUE SÃO ARRANJOS SIMPLES DE 4 ELEMENTOS TOMADOS DE 2 A 2
[tex]A_{n,p}=\frac{n!}{(n-p)!}\\\\\\A_{4,2}=\frac{4!}{(4-2)!}\\\\\\A_{4,2}=\frac{4\cdot3\cdot2!}{2!}\\\\\\A_{4,2}=4\cdot3\\\\\boxed{A_{4,2}=12}[/tex]